Methods that are currently available for study of steroid receptors depend on the binding of the radiolabeled steroid to receptor. This interaction is not covalent, hence, studies on the structure of the receptor have been limited. The objective of this research plan is to produce monoclonal antibodies against the various functional domains of purified rabbit uterine progesterone receptor. This would allow detailed study of receptor structure-function relationships using a method which does not depend on binding a [3H]ligand to receptor. The specific aims are to purify progesterone receptor from rabbit uterus using hydrophobic and affinity chromatography; to immunize mice in vivo or murine spleen cells in vitro; to produce hybridomas of the immunized cells and to clone the receptor-specific hybridomas. A library of monoclonal antibodies against specific functional domains of the progesterone receptor will be obtained. The antibodies will be characterized with respect to species, cross-reactivity, and specificity, and will be used to study the structural aspects of the receptor using glycerol gradients, Western blotting and limited proteolysis of receptor. In the future, antibodies against progesterone receptor could be used as a diagnostic tool for identifying hormone-dependent breast cancer; to isolate the mRNA coding for receptor and, ultimately, the gene for progesterone receptor could be cloned. Finally, antibodies against progesterone receptor will be powerful to gain insight into the interaction of this regulatory molecule with specific progesterone induced genes.